Lanthanide-based catalyst systems may be useful for polymerizing conjugated diene monomers to form polydienes having high cis-1,4-linkage contents. The resulting cis-1,4-polydienes may display pseudo-living characteristics in that, upon completion of the polymerization, some of the polymer chains may possess reactive ends that can react with certain functionalizing agents to yield functionalized polymers. Also, the cis-1,4-polydienes prepared with lanthanide-based catalysts have a linear backbone structure, which is believed to provide better tensile properties, higher abrasion resistance, lower hysteresis loss, and better fatigue resistance than those of analogous polymers prepared with other catalyst systems such as titanium-based, cobalt-based, and nickel-based catalyst systems. The cis-1,4-polydienes prepared with lanthanide-based catalyst systems are particularly suitable for use in tire components such as sidewalls and treads.